The invention relates to a guiding device of a machine processing sheet-like print carriers, in particular of a sheet-processing printing machine, the guiding device having a guide surface, over and beyond which sheets are drawn, during operation, simultaneously with positive guidance by a margin of the sheets which, respectively, extends in a direction of sheet travel, and having nozzles terminating in the guide surface, for conducting therethrough, during operation, a flow of air for forming an air cushion between the guide surface and the respective sheet; the invention also related to a machine for processing sheet-like print carriers, which is equipped with a guiding device of the foregoing type.
A guiding device of the type mentioned hereinbefore has become known, for example, from the published German Patent Document DE 42 09 067 C2, which corresponds to pending U.S. patent application Ser. No. 09/699,981. This document considers the problem wherein a sheet, which is drawn over and beyond an air cushion located between the latter and the guide surface, assumes an insufficient suspension or flotation height in jeopardized zones. It has become clear that one of these jeopardized zones is the sheet margins which extend lateral to the direction of travel of the sheets.
In order to ensure a sufficient flotation height in zones of lateral margins of the sheets, it is proposed, in the aforementioned publication, that, according to a first embodiment, blocking bars be arranged on the guide surface along the sheet side edges. According to a second embodiment, lateral blowers are provided, which blow under the outer margins of a respective sheet from the outside. With these embodiments, a build-up of air is generated under the sheet and increases the flotation height of the latter. In both of the aforementioned instances, setting operations are necessary in order to adapt to the format of the print carrier to be processed.
It is accordingly an object of the invention to provide a guiding device of a machine for processing planar print carriers which is based upon the construction of the guiding device initially mentioned in the introduction hereto, so that, in order to guide sheet-like print carriers of varying format over the guide surface, there is no need for any aids which have to be adjusted in order to adapt to the respective format.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a guiding device of a machine for processing planar print carriers, the guiding device having a guide surface, over and beyond which sheets are drawn, during operation, simultaneously with positive guidance by a margin of the sheets, which, respectively, extends in a direction of sheet travel, and having nozzles terminating in the guide surface, for conducting therethrough, during operation, a flow of air for forming an air cushion between the guide surface and the respective sheet, comprising a region with a closed surface located on the guide surface, on the path of the print carrier along the guide surface, the region being disposed opposite a respective margin of a processable one of the print carriers of varying format, the margin extending laterally with respect to the direction of sheet travel.
In accordance with another feature of the invention, the nozzles, when a flow passes through them, during operation, serves for generating flows aligned with the lateral margins of the print carriers, the nozzles being restricted to a region which has, transversely to the direction of sheet travel, an extent lying within an extent which is transverse to the direction of sheet travel and which has a print carrier with a smaller format than a print carrier with the largest processable format.
In accordance with a further feature of the invention, the nozzles, when a flow passes through them, during operation, serves for generating flows oriented perpendicularly to the lateral margins.
In accordance with an added feature of the invention, the nozzles lie within an extent, transverse to the direction of travel of a print carrier having the smallest possible format suitable for processing.
In accordance wit a concomitant aspect of the invention, there is provided a machine for processing planar print carriers, including a guiding device having a guide surface, over and beyond which sheets are drawn, during operation, simultaneously with positive guidance by a margin of the sheets, which, respectively, extends in a direction of sheet travel, and having nozzles terminating in the guide surface, for conducting therethrough, during operation, a flow of air for forming an air cushion between the guide surface and the respective sheet, the guiding device comprising a region with a closed surface located on the guide surface, on the path of the print carrier along the guide surface, the region being disposed opposite a respective margin of a processable one of the print carriers of varying format, the margin extending laterally with respect to the direction of sheet travel.
To achieve the foregoing objectives, on the path of the print carrier along the guide surface, there is provided on the latter a region with a closed surface located opposite a respective margin of the processable print carriers of varying format, the margin being lateral with respect to the direction of travel.
This construction is based upon the recognition that an underpressure is formed in the mouth or outlet regions of nozzles which open into the guide surface and through which a flow passes in order to produce an air cushion between the guide surface and a sheet drawn over and beyond the latter and an overpressure necessary for the suspended or floating guidance of the sheet is built up only at some distance from the respective mouth or outlet region. A construction according to the invention avoids the situation wherein a margin of any one of the processable print carriers of varying format, the margin being lateral with respect to the direction of travel, comes into the range of influence of the underpressure in the mouth or outlet regions of the nozzles.
In order to implement this, however, it is clearly possible to place the nozzles so that, when a format smaller than the maximum possible format is being processed, some of the nozzles are arranged outside the lateral margins of the smaller format.
In a preferred embodiment, there is a provision for nozzles, when a flow passes operationally through them, to generate flows aligned with the lateral margins of the print carriers and to be restricted to a region which has, transversely to the direction of sheet travel, an extent lying within an extent which is transverse to the direction of sheet travel and which has a print carrier with a smaller format than a print carrier with the largest processable format.
A further preferred embodiment provides for the nozzles, when a flow passes operationally through them, to generate flows oriented perpendicularly to the lateral margins.
According to a preferred development, there is provision for the nozzles to lie within an extent, transverse to the direction of sheet travel, of a print carrier having the smallest possible format suitable for processing.
This embodiment combines within it partly production-related and partly functional benefits which go beyond the construction necessary for achieving the objective presented herein.
A preferred restriction of the nozzles to only two nozzle rows within the smallest format requires a comparatively low outlay in terms of construction for supplying the nozzles with blowing or blast air, when compared with supplying conventional nozzles distributed over wide regions of a guide surface. Furthermore, particularly when the nozzles are preferably closely adjacent to one another in each of the nozzle rows, the nozzle orientation that is provided affords a functional advantage inasmuch as a pressure profile below the respective sheet is consequently virtually constant in the direction of sheet travel, so that a pressure profile occurring below a respective sheet gives rise, transversely to the direction of sheet travel, to an effect which is desirable per se, specifically that of stiffening the respective sheet in the direction of travel. This has, however, a steadying effect upon the travel of the sheet along the guide surface.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a guiding device of a machine processing planar print carriers, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: